Process for producing a composite tube

ABSTRACT

A tube of fiber-reinforced plastic has a fitting face. A process for producing the tube includes the following steps: a) winding a fiber reinforcing material onto a winding core and applying a matrix material to form the tube; b) centering a fitting shaping tool in relation to the winding core; c) pushing the fitting shaping tool in the axial direction onto the later fitting face, which is formed on an annular part of the external circumferential face of the tube, wherein the fitting shaping tool rotates relative to the tube and to the winding core at least temporarily as it is being pushed on; d) thermally treating the tube in a furnace to cure the matrix material. The shaping tool remains in contact with the part of the external circumferential face during the thermal treatment and generates a defined surface on the outer side of the tube.

The invention relates to a process for producing a tube made offiber-reinforced plastic, in which the tube is formed by winding a fiberreinforcing material onto a winding core and applying a matrix material,and to a tube produced in this way.

Such processes are already familiar, for example, for the production ofrolls of composite material. The winding core in this case defines theinternal surface of the tube and generates a corresponding surfaceaccuracy and surface quality. The outer side of the tube retains anirregular curvature after winding and curing in the furnace. Mechanicalfinishing has until now been necessary in order to generate a defined,smooth surface on the outer side of the tube. A corresponding surface isgenerated either by turning or by grinding. This is disadvantageous,since additional elaborate processing steps are necessary. Only matrixmaterial can be removed, furthermore, since the fiber reinforcement mustnot be damaged. This imposes a limitation on the design.

Also familiar from DE 2342593 A is a process for producing conical tubesfrom glass fiber-reinforced polyester resin, in which it is possible todispense with subsequent machining of the surface. After winding thetube onto a winding core, and before curing, a press sleeve is appliedfrom the outer side or is pushed on axially for the entire length of thetube, so that the tube material is compressed. It is then cured. Adisadvantage associated with this familiar process is that noparticularly accurate surfaces can be produced. There is also norequirement for this, however, for tubes that are used as masts.

The object of the invention is to further develop a process forproducing wound tubes from fiber-reinforced plastic such that preciselydefined surfaces can be generated on the outer side without subsequentmechanical finishing.

According to the invention, the object for the process is accomplishedin that the following steps are carried out in the process for producinga tube from fiber-reinforced plastic having a fitting face:

a) winding a fiber reinforcing material onto a winding core and applyinga matrix material to form the tube,

b) centering a fitting shaping tool in relation to the winding core,

c) pushing the fitting shaping tool in the axial direction onto thelater fitting face, which is formed on an annular part of the externalcircumferential face of the tube, wherein the fitting shaping toolrotates relative to the tube and to the winding core at leasttemporarily as it is being pushed on,

d) thermally treating the tube in a furnace to cure the matrix material,wherein the fitting shaping tool remains in contact with the annularpart of the external circumferential face during the thermal treatmentand, as a result, a defined surface (fitting surface) is generated bythe fitting shaping tool on the outer side of the tube.

An advantage of this process is that the defined surface is embossedinto the still formable matrix material by the fitting shaping toolprior to curing and is cured in the furnace in this form. A highlyuniform and problem-free displacement or compaction of surplus matrixmaterial is achieved by the pushing-on of the fitting shaping tool andby the associated, at least temporary, relative rotational movementbetween the fitting shaping tool and the tube. Very accurate faces, e.g.with a very smooth, even surface or with a precise diameter or with aprecisely defined form, are possible as a result. An accurate coaxialform of the fitting face is assured by the fact that the fitting shapingtool is centered in relation to the winding core. Centering is carriedout in such a way that it continues to be effective during thepushing-on operation. Centering preferably takes place as mechanicalcentering, for example by means of a centering pin which engages in acentering bore.

Such precise fitting faces are necessary as the basis for effectiveclamped or bonded connections, for example with metallic connectingcomponents. Tubes having a surface which fits precisely internally andexternally can be produced in a simplified manner by the processaccording to the invention. The inner side is determined by the windingcore, and the annular region on the outer face is determined by thefitting shaping tool. Since this is possible without mechanicalfinishing, the tubes can be produced more rapidly and more costeffectively. The relative rotational movement can be achieved either byrotation of the fitting shaping tool or by rotation of the tube, e.g. byrotation of the winding core. Both parts can also rotate at a differentspeed or direction of rotation. The pushing-on process can take placeeither by active movement of the fitting shaping tool and/or by activemovement of the tube.

The process according to the invention is particularly suitable forproducing tubes with a fitting face, which exhibit an external diameterof between 30 and 500 mm, and preferably of between 80 and 300 mm, inthe region of the fitting face, this diameter exhibiting a deviationfrom the nominal value of less than +/− 0.5 mm, and preferably of lessthan +/− 0.1 mm, in the region of the annular fitting face. It is alsoparticularly suitable for producing tubes with a conically shapedfitting face, its cone angle being between 0.1° and 5°, and preferablybetween 0.1° and 1°, and the deviation from the nominal value of thecone angle being less than +/− 0.2°, and preferably less than +/− 0.05°.

A fiber reinforcement material made of glass fibers or aramide fibersor, most preferably, of carbon fibers is used for the production of thetube. Various other fibers can also be used. The fiber reinforcement canbe applied at different angles and in several layers. In the process,the fibers are applied in the form of a winding of one or a plurality ofparallel rovings or of woven tapes or mesh tapes respectively in asingle layer or multiple layers or also in combination. The fiberreinforcement is surrounded by a plastic matrix. Thermoplastics orpreferably thermosetting plastics, such as epoxy resin, are particularlysuitable as a matrix material. The matrix material may already bepresent on the fiber reinforcement before winding, or it may be appliedduring or after winding. The curing or consolidation of the matrixmaterial takes place by thermal treatment in the furnace, preferably ata temperature between 50° C. and 250° C.

Further advantageous characterizing features of the process according tothe invention, which further improve the quality and the designpossibilities of the surface or which simplify the process, can be foundin the dependent claims.

Steps a)-d) are preferably carried out in the indicated sequence.However, individual steps can also be carried out in a differentsequence or partly in parallel. For example, step b) can accordingly becarried out before step a) or in parallel to step c). The application ofthe matrix material in full or in part could also take place only duringstep c).

In any event, the fitting shaping tool is configured in such a way thatit encloses the tube in its entirety in an annular region. Applicationsof the process according to the invention are also possible, however, inwhich the fitting shaping tool only bears against one part of thecircumference with the intention that defined fitting faces are to begenerated only on this part. The result is an interrupted annularfitting face. The fitting shaping tool preferably bears against a largepart of the circumference on the surface of the tube, so that thefitting face is generated in a defined manner on a large part of thecircumference. The expression large part is used to denote more thanhalf, and preferably more than 70%, of the circumference. In particular,the fitting shaping tool can be in contact with the tube over its entirecircumference in order to generate a continuous annular fitting face.

In the case of tapered, conical or curved faces, the fitting shapingtool can be configured in a single piece, for example; a simple,seam-free surface is thus possible. It may be of two-part or multi-partconfiguration in order to make it easier to apply and remove the fittingshaping tool, including in the case of conical or curved faces, or inorder to be able to generate cylindrical or only slightly conicallyformed fitting faces. The individual parts of the fitting shaping toolare joined together prior to pushing on. Crushing of the metric materialand inaccurate surface formation are avoided as a result. In this case,too, seam-free formation of the surface is assured by the relativerotation in the course of pushing on.

In order for controlled heating and associated effective curing also tobe assured in the region of the fitting shaping tool, it is advantageousfor the fitting shaping tool to be heated before or after it is broughtinto contact with the tube. Heating can take place, for example, bymeans of electrical heating cartridges inserted into holes in thefitting shaping tool. A cold fitting shaping tool would require a longerholding time in the furnace. The fitting shaping tool can also be heatedprior to application and only then brought into contact with the tube.Heating can take place, for example, in a furnace or by means of someother heat source, such as with IR radiators.

A temperature sensor can be used in order to be able to monitor thetemperature of the fitting shaping tool in the course of production ofthe fitting face, and/or a temperature controller can be used forheating the fitting shaping tool. This ensures that the matrix materialis heated within a desired temperature window. An excessively lowtemperature will lead to insufficient curing, and an excessively hightemperature can damage the matrix material and alter its properties inan undesired manner.

The fitting shaping tool can be configured in such a way that itgenerates a cylindrical surface having a constant diameter on the tube.A fitting seat for a further component, which is subsequently mounted onthe tube, can thus be produced directly in this way. The process isparticularly suitable for producing conical fitting faces at the end ofthe tube. The fitting shaping tool is formed in such a way for thispurpose that it generates a conical surface on the tube (11). Thediameter of the conical face preferably decreases towards the end of thetube. Conical fitting faces are suitable in particular in order to beable to produce an effective clamped connection between the tube andsubsequently installed metal connectors, of the kind that are used, forexample, in drill pipes for oil drilling. Fitting faces that are alsonot straight in their cross section can be generated with the process,for example a curved surface having a defined radius of curvature on thetube. The wave can exhibit a regular waveform. The advantage of suchfaces is that a certain axial force can be observed in the connection ofthe tube to other components. Fitting shaping tools can also be usedwhich exhibit a combination of the previously mentioned fitting faces,which thus possess a cylindrical part and a conical part, for example.

In order to be able to produce tubes with high strength, carbon fiberswhich are preferably wrapped in the form of rovings are preferably usedas a fiber reinforcement material. In particular in the case of veryhigh strength requirements, it is advantageous if no mechanical surfacemachining is necessary, since the fibers in this case must not beexposed or damaged under any circumstances. The process finds aparticularly advantageous application if the matrix material is athermosetting plastic, in particular an epoxy resin. Curing temperaturesof between 50° C. and 250° C. are necessary for this purpose.

Thermosetting plastics produce a hard surface, so that the savedmechanical machining has a particularly noticeable effect here.

If the fitting shaping tool is pressed against the externalcircumferential face, additional compaction can be achieved in thisannular part of the tube, which further increases the strength and theload-bearing capacity. It is preferably pressed with a pressure that isgreater than 0 bar and is up to 1 bar.

In the case of the tube according to the invention, the object isaccomplished in that the tube is produced by the process according tothe invention.

It is particularly preferable for the tube to be configured in such away that it exhibits an external diameter of between 30 and 500 mm, andpreferably of between 80 and 300 mm, in the region of the fitting face,this diameter exhibiting a deviation from the nominal value of less than+/− 0.5 mm, and preferably of less than +/− 0.1 mm, in the region of theannular fitting face. It is also particularly preferable for the tube toexhibit a conically shaped fitting face, the cone angle of which isbetween 0.1° and 5°, and preferably between 0.1° and 1°, and in whichthe deviation from the nominal value of the cone angle is less than +/−0.2°, and preferably less than +/− 0.05°.

Further advantageous characterizing features of the invention aredescribed below on the basis of illustrative embodiments with referenceto the drawings. The aforementioned characterizing features are capableof being implemented advantageously not only in the depictedcombination, but also when combined individually with one another.

FIG. 1 Tube with a cylindrical tool for the process according to theinvention

FIG. 2 Tube with a conical tool for the process according to theinvention

FIG. 3 Tube element for drill pipes with a CRP tube produced accordingto the process according to the invention.

The figures are described below in more detail. FIG. 1 depicts a detailas an example of the production of a tube having a cylindrical fittingface. The tube 1 is preferably made of CRP (Carbon Fiber-ReinforcedPlastic). The center line 7 indicates that only the upper half isrepresented in cross section. The tube has been wound onto the windingcore 8 by winding fiber material, for example rovings or woven tapes ormesh tapes, in one or more layers, and by applying matrix material, forexample thermosetting resin. The winding core 8 defines the inner faceand determines the internal diameter 3. If necessary, the inner face canalso be conical in shape.

The fitting shaping tool 2 has been pushed onto the still-formablematrix material of the tube 1 after winding while rotating at leasttemporarily relative to the tube in the axial direction A. The fittingshaping tool can preferably be heated and can be combined with atemperature sensor and/or a temperature controller. An annularcylindrical fitting face 6 is produced in the region of the contact facebetween the fitting shaping tool and the tube 1. The fitting face isformed precisely in the desired form as a result of the fitting shapingtool being applied prior to curing and remaining on the tool duringcuring in the furnace. An accurate and problem-free embodiment of thedesired fitting face is made possible by pushing on while rotating atleast temporarily. Before pushing on, the fitting shaping tool wascentered in relation to the winding core 8, for example by means of acentering pin which engages in a centering bore. This involves carryingout the centering, which is not depicted here, in such a way that thefitting shaping tool remains centered during the pushing-on process. Therest of the outer face 5 of the tube remains imprecise in this example,in the form in which it emerges after winding the tube. After shapingthe fitting face, the tube 1 is cured in contact with the fittingshaping tool 2 in a furnace.

FIG. 2 depicts a similar example of the production of a conical fittingface. The center line 17 is indicated in this case, too. The tube 11 iswound onto a winding core 18 tapering towards the end of the tube, whichdetermines the inner face 13 in a defined manner. The fitting shapingtool 12, which in this case, too, has been pushed on while rotating atleast temporarily in the axial direction A, likewise generates on theouter side of the tube a cone 16 having a precisely defined conicalsurface 14 tapering towards the end of the tube. In this case, too, thefitting shaping tool 2 was centered in relation to the winding core 8before pushing on, for example by means of a centering pin which engagesin a centering bore.

The centering, which is not depicted here, is carried out in such a waythat the fitting shaping tool 12 remains centered during the pushing-onprocess. The wound surface next to the tool 12 remains untreated herefor the time being. After shaping the fitting face, the tube 11 is curedin contact with the fitting shaping tool 12 in a furnace.

An example of an application is depicted in FIG. 3. This is a tubularelement, of the kind that can be used for the assembly of a drill pipefor oil drilling. In this case, a metal connector 20, which exhibits atapered thread 24 for screwing together with further tube elements toform a string, must be connected to the CRP tube 11 a. The connectionmust be capable of transmitting high torques and axial forces. In orderto make this possible, the metal connector 20 is connected to acounter-sleeve 21 via a cylindrical screwed connection 22 and a lockingelement in the form of a subsequently introduced pin. The end of thetube 11 a is clamped between the counter-sleeve 21 and the metalconnector 20. Adequate clamping forces can be generated because of theconical shape. Precise conical fitting faces are required on the innerside and the outer side of the tube, however, for a good connection. Theinner fitting face 23 is produced via the winding core in the course ofproduction. The outer fitting face 16 a via the process according to theinvention with a fitting shaping tool, as described above. Furtherpossible applications for the production process present themselves forother tube connections or for add-on components which are dependent on aprecise external surface of the tube.

LIST OF REFERENCE DESIGNATIONS

-   1, 11, 11 a CRP tube-   2, 12 fitting shaping tool-   3 internal diameter of the CRP tube-   4 external diameter for the fitting face-   5, 15 outer face of the CRP tube-   6, 16, 16 a fitting face-   7, 17 center-line of CRP tube-   8, 18 winding core-   13 inner face of the CRP tube-   14 conical face of the fitting face-   20 metal connector-   21 counter-sleeve-   22 cylindrical screwed connection-   23 inner fitting face of the CRP tube-   24 tapered thread-   25 locking pin-   A axial direction of the pushing-on movement

1-15. (canceled)
 16. A process for producing a tube of fiber-reinforcedplastic having a fitting face, the process comprising the followingprocess steps: a) winding a fiber reinforcing material onto a windingcore and applying a matrix material to form the tube; b) centering afitting shaping tool relative to the winding core; c) pushing thefitting shaping tool in an axial direction onto a fitting face to beformed, the fitting face to be formed on an annular part of an externalcircumferential face of the tube, and thereby rotating the fittingshaping tool at least temporarily relative to the tube and to thewinding core as the fitting shaping tool is being pushed on; d)thermally treating the tube in a furnace to cure the matrix material,maintaining the fitting shaping tool in contact with the part of theexternal circumferential face during the thermal treatment to generate adefined surface on the outer side of the tube by the fitting shapingtool.
 17. The process according to claim 16, which comprises carryingout steps a) to d) one after another in a sequence a) then b) then c)then d).
 18. The process according to claim 16, wherein the fittingshaping tool is a two-part tool with two parts, and the method comprisesjoining the two parts of the tool together prior to step b).
 19. Theprocess according to claim 16, wherein the fitting shaping tool is amulti-part tool with a plurality of parts, and the method comprisesjoining the plurality of parts of the tool together prior to step b).20. The process according to claim 16, which comprises heating thefitting shaping tool before or while the tool is brought into contactwith the tube.
 21. The process according to claim 20, wherein thefitting shaping tool is a heated tool that had been heated previouslybefore the tool is brought into contact with the tube.
 22. The processaccording to claim 20, which comprises using a temperature sensor on thefitting shaping tool and/or using a temperature controller for heatingthe fitting shaping tool.
 23. The process according to claim 16, whereinthe fitting shaping tool is configured to generate a cylindrical surfacehaving a constant external diameter on the tube.
 24. The processaccording to claim 16, wherein the fitting shaping tool is configured togenerate a conical surface on the tube.
 25. The process according toclaim 16, wherein the fitting shaping tool is configured to generate acurved surface with a defined radius of curvature on the tube.
 26. Theprocess according to claim 16, wherein the fiber reinforcing material isselected from the group consisting of carbon fibers, glass fibers. andaramide fibers.
 27. The process according to claim 26, wherein thefibers of the reinforcing material are wrapped onto the winding core inthe form of rovings.
 28. The process according to claim 16, wherein thematrix material is a thermosetting plastic.
 29. The process according toclaim 16, wherein the matrix material is an epoxy resin.
 30. The processaccording to claim 16, which comprises pressing the fitting shaping toolagainst the external circumferential face with a pressure that isgreater than 0 bar and no more than 1 bar.
 31. A tube, comprising a tubebody of fiber-reinforced plastic formed with an annular fitting faceproduced in a process according to claim
 16. 32. The tube according toclaim 31, wherein said tube has an external diameter in a region of saidfitting face between 30 and 500 mm and the diameter deviates from thenominal value by less than +/− 0.5 mm in the region of the annularfitting face.
 33. The tube according to claim 32, wherein the externaldiameter in the region of said fitting face lies between 80 and 300 mm,and the diameter deviates from the nominal value by less than +/− 0.1 mmin the region of the annular fitting face.
 34. The tube according toclaim 31, wherein said fitting face is conically shaped, with a coneangle between 0.1 ° and 5°, and wherein a deviation from the nominalvalue of the cone angle is less than +/− 0.2°.
 35. The tube according toclaim 34, wherein the cone angle lies between 0.1 ° and 1°, and thedeviation from the nominal value of the cone angle is less than +/− 0.05°.